My bank sold a local branch to another bank (in the state of Wisconsin, United States of America), including my accounts, without my permission. My first knowledge of it was that my debit card was declined. Calling my local branch during business hours only got an answering machine under the new bank's name.
I went home, checked 8 months or so of envelopes from the bank, and saw zero pertinent information.
Today I finally got through to a human at my old bank's customer service. Their position: you are no longer a customer, we don't have your accounts. Would you like the new bank's customer service number?
And, yes, I got middle-sized envelopes from my "new owner" twice over the last month. I didn't open them, just as I don't open the offers from other banks that I'm not a member of, insurance companies I have no policies with, car repair scams, etc.